Envelope alignment calibration in radio frequency systems

ABSTRACT

Apparatus and methods for envelope alignment calibration in radio frequency (RF) systems are provided. In certain embodiments, calibration is performed by providing an envelope signal that is substantially triangular along an envelope path, and by providing an RF signal to a power amplifier along an RF signal path. Additionally, an output of the power amplifier is observed to generate an observation signal using an observation receiver. The observation signal includes a first peak and a second peak, and a delay between the envelope signal and the RF signal is controlled based on relative size of the peaks of the observation signal to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/449,511, filed Sep. 30, 2021 and titled “ENVELOPE ALIGNMENTCALIBRATION IN RADIO FREQUENCY SYSTEMS,” which is a continuation of U.S.application Ser. No. 16/946,844, filed Jul. 8, 2020 and titled “ENVELOPEALIGNMENT CALIBRATION IN RADIO FREQUENCY SYSTEMS,” which claims thebenefit of priority under 35 U.S.C. § 119 of U.S. Provisional PatentApplication No. 62/871,881, filed Jul. 9, 2019 and titled “ENVELOPEALIGNMENT CALIBRATION IN RADIO FREQUENCY SYSTEMS,” each of which isherein incorporated by reference in its entirety.

BACKGROUND Field

Embodiments of the invention relate to electronic systems, and inparticular, to power amplifiers for radio frequency electronics.

Description of the Related Technology

Radio frequency (RF) communication systems can be used for transmittingand/or receiving signals of a wide range of frequencies. For example, anRF communication system can be used to wirelessly communicate RF signalsin a frequency range of about 30 kHz to 300 GHz, such as in the range ofabout 410 MHz to about 7.125 GHz for fifth generation (5G)communications using Frequency Range 1 (FR1).

Examples of RF communication systems include, but are not limited to,mobile phones, tablets, base stations, network access points,customer-premises equipment (CPE), laptops, and wearable electronics.

SUMMARY

In certain embodiments, the present disclosure relates to a method ofcalibrating for envelope alignment. The method includes providing anenvelope signal with a peak along an envelope path to an envelopecontrolled circuit, providing a radio frequency signal with a first pairof peaks to a power amplifier along a radio frequency signal path,observing an output of the power amplifier to generate an observationsignal including a second pair of peaks corresponding to the first pairof peaks of the radio frequency signal, and calibrating a delay betweenthe envelope signal and the radio frequency signal based on comparing asize of a first peak of the second pair of peaks to a size of a secondpeak of the second pair of peaks.

In various embodiments, the method further includes changing the delayuntil the size of the first peak is substantially equal to the size ofthe second peak.

In several embodiments, calibrating the delay includes controlling adelay of a controllable delay circuit along the envelope path.

In some embodiments, the method further includes observing the output ofthe power amplifier after a duplexer.

In a number of embodiments, calibrating the delay includes programmingcalibration data into a memory.

In various embodiments, the envelope controlled circuit includes acharge pump. According to several embodiments, the method furtherincludes generating a regulated voltage based on the envelope signalusing the charge pump, providing a radio frequency output signal fromthe output of the power amplifier to a radio frequency switch, andcontrolling a turn on voltage of the radio frequency switch using theregulated voltage.

In a number of embodiments, the envelope controlled circuit includes anenvelope tracker. According to some embodiments, the method furtherincludes changing a supply voltage of the power amplifier in relation tothe envelope signal using the envelope tracker. In accordance withseveral embodiments, the envelope controlled circuit further includes acharge pump, the method further including controlling a delay betweenthe envelope signal arriving to the charge pump and the envelope signalarriving to the envelope tracker using a controllable delay circuit.According to various embodiments, the method further includes increasinga channel capacity of the radio frequency signal path by calibrating adelay between the envelope signal and the radio frequency signal.

In several embodiments, the envelope signal for calibrating for envelopealignment is substantially triangular, the peak of the envelope signalcorresponding to a peak of a triangle.

In some embodiments, the first pair of peaks are each of substantiallyequal in size.

In various embodiments, the radio frequency signal for calibrating forenvelope alignment is substantially triangular, the first pair of peaksof the radio frequency signal corresponding to peaks of a pair oftriangles.

In a number of embodiments, the method further includes observing theoutput of the power amplifier after a filter, and calibrating atransceiver to compensate for the filter.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a front end system including anenvelope controlled circuit and a power amplifier, a baseband processorconfigured to provide an envelope signal with a peak along an envelopepath to the envelope controlled circuit, and a transceiver configured toprovide a radio frequency signal with a first pair of peaks to the poweramplifier along a radio frequency signal path, the transceiver includingan observation receiver configured to process an observation signalcaptured from an output of the power amplifier, the observation signalincluding a second pair of peaks corresponding to the first pair ofpeaks of the radio frequency signal, the observation receiver furtherconfigured to generate calibration data based on comparing a size of afirst peak of the second pair of peaks relative to a size of a secondpeak of the second pair of peaks, the calibration data operable tocalibrate a delay between the envelope signal and the radio frequencysignal.

In various embodiments, the transceiver is further configured to controlthe delay until the size of the first peak is substantially equal to thesize of the second peak.

In a number of embodiments, the front end system further includes acontrollable delay circuit along the envelope path, the calibration dataoperable to control a delay of the controllable delay circuit.

In several embodiments, the front end system further includes aduplexer, the observation signal generated after the duplexer.

In various embodiments, the front end system includes a directionalcoupler configured to generate the observation signal.

In a number of embodiments, the mobile device further includes a memorystoring the calibration data.

In some embodiments, the envelope controlled circuit includes a chargepump. According to various embodiments, the charge pump is configured togenerate a regulated voltage based on the envelope signal, the front endsystem further including a radio frequency switch configured to receivea radio frequency output signal from the output of the power amplifierand having a turn on voltage controlled by the regulated voltage.

In various embodiments, the envelope controlled circuit includes anenvelope tracker. According to a number of embodiments, the envelopetracker is configured to change a supply voltage of the power amplifierin relation to the envelope signal. In accordance with severalembodiments, the envelope controlled circuit further includes a chargepump, the front end circuit further including a controllable delaycircuit operable to control a delay between the envelope signal arrivingto the charge pump and the envelope signal arriving to the envelopetracker.

In a number of embodiments, the envelope signal for calibrating forenvelope alignment is substantially triangular, the peak of the envelopesignal corresponding to a peak of a triangle.

In several embodiments, the first pair of peaks are each ofsubstantially equal in size.

In various embodiments, the radio frequency signal for calibrating forenvelope alignment is substantially triangular, the first pair of peaksof the radio frequency signal corresponding to peaks of a pair oftriangles.

In certain embodiments, the present disclosure relates to a radiofrequency front end system. The radio frequency front end systemincludes an envelope controlled circuit configured to receive anenvelope signal with a peak along an envelope path, a power amplifierconfigured to receive a radio frequency signal with a first pair ofpeaks along a radio frequency signal path, a directional couplerconfigured to generate an observation signal based on observing anoutput of the power amplifier, the observation signal including a secondpair of peaks corresponding to the first pair of peaks of the radiofrequency signal, and an observation receiver configured to process theobservation signal to generate calibration data based on comparing asize of a first peak of the second pair of peaks relative to a size of asecond peak of the second pair of peaks, the calibration data operableto calibrate a delay between the envelope signal and the radio frequencysignal.

In various embodiments, the transceiver is further configured to controlthe delay until the size of the first peak is substantially equal to thesize of the second peak. According to a number of embodiments, the radiofrequency front end system further includes a controllable delay circuitalong the envelope path, the calibration data operable to control adelay of the controllable delay circuit.

In several embodiments, the radio frequency front end system furtherincludes a duplexer, the observation signal generated after theduplexer.

In a number of embodiments, the radio frequency front end system furtherincludes a memory storing the calibration data.

In various embodiments, the envelope controlled circuit includes acharge pump. According to several embodiments, the charge pump isconfigured to generate a regulated voltage based on the envelope signal,the radio frequency front end system further including a radio frequencyswitch configured to receive a radio frequency output signal from theoutput of the power amplifier and having a turn on voltage controlled bythe regulated voltage.

In a number of embodiments, the envelope controlled circuit includes anenvelope tracker. According to some embodiments, the envelope tracker isconfigured to change a supply voltage of the power amplifier in relationto the envelope signal. In accordance with various embodiments, theenvelope controlled circuit further includes a charge pump, the frontend circuit further including a controllable delay circuit operable tocontrol a delay between the envelope signal arriving to the charge pumpand the envelope signal arriving to the envelope tracker.

In several embodiments, the envelope signal for calibrating for envelopealignment is substantially triangular, the peak of the envelope signalcorresponding to a peak of a triangle.

In some embodiments, the first pair of peaks are each of substantiallyequal in size.

In various embodiments, the radio frequency signal for calibrating forenvelope alignment is substantially triangular, the first pair of peaksof the radio frequency signal corresponding to peaks of a pair oftriangles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one example of a communication network.

FIG. 2A is a schematic diagram of one example of a communication linkusing carrier aggregation.

FIG. 2B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 2A.

FIG. 2C illustrates various examples of downlink carrier aggregation forthe communication link of FIG. 2A.

FIG. 3A is a schematic diagram of one example of a downlink channelusing multi-input and multi-output (MIMO) communications.

FIG. 3B is schematic diagram of one example of an uplink channel usingMIMO communications.

FIG. 3C is schematic diagram of another example of an uplink channelusing MIMO communications.

FIG. 4 is a schematic diagram of a radio frequency (RF) switch systemaccording to one embodiment.

FIG. 5A is a schematic diagram of a positive charge pump according toone embodiment.

FIG. 5B is a schematic diagram of a charge pump stage according to oneembodiment.

FIG. 6A is a schematic diagram of a positive charge pump according toanother embodiment.

FIG. 6B is a schematic diagram of one example of a ring oscillator forgenerating clock signals for a charge pump.

FIG. 6C is one example of a timing diagram of clock signals for the ringoscillator of FIG. 6B.

FIG. 7 is a schematic diagram of a positive charge pump according toanother embodiment.

FIG. 8 is a schematic diagram of a negative charge pump according to oneembodiment.

FIG. 9 is a schematic diagram of a level shifter according to oneembodiment.

FIG. 10 is a schematic diagram of an RF switch network according toanother embodiment.

FIG. 11 is a schematic diagram of one embodiment of a calibration schemefor a communication system operating with envelope tracking.

FIG. 12A is a schematic diagram of one embodiment of a front end modulecoupled to an antenna.

FIG. 12B is a plot of one example of an in-band frequency response for aduplexer of the front end module of FIG. 12A.

FIG. 13 is a schematic diagram of one embodiment of an envelope signalinterface.

FIG. 14 is an annotated diagram of an envelope tracking system inrelation to Shannon's theorem.

FIG. 15 is a schematic diagram of a front end system according toanother embodiment.

FIG. 16 is a schematic diagram of one embodiment of a mobile device.

FIG. 17 is a schematic diagram of one embodiment of a communicationsystem for transmitting RF signals.

FIG. 18 is a schematic diagram of one example of a power amplifiersystem including an envelope tracker.

FIG. 19A shows a first example of a power amplifier supply voltageversus time.

FIG. 19B shows a second example of a power amplifier supply voltageversus time.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

The International Telecommunication Union (ITU) is a specialized agencyof the United Nations (UN) responsible for global issues concerninginformation and communication technologies, including the shared globaluse of radio spectrum.

The 3rd Generation Partnership Project (3GPP) is a collaboration betweengroups of telecommunications standard bodies across the world, such asthe Association of Radio Industries and Businesses (ARIB), theTelecommunications Technology Committee (TTC), the China CommunicationsStandards Association (CCSA), the Alliance for TelecommunicationsIndustry Solutions (ATIS), the Telecommunications Technology Association(TTA), the European Telecommunications Standards Institute (ETSI), andthe Telecommunications Standards Development Society, India (TSDSI).

Working within the scope of the ITU, 3GPP develops and maintainstechnical specifications for a variety of mobile communicationtechnologies, including, for example, second generation (2G) technology(for instance, Global System for Mobile Communications (GSM) andEnhanced Data Rates for GSM Evolution (EDGE)), third generation (3G)technology (for instance, Universal Mobile Telecommunications System(UMTS) and High Speed Packet Access (HSPA)), and fourth generation (4G)technology (for instance, Long Term Evolution (LTE) and LTE-Advanced).

The technical specifications controlled by 3GPP can be expanded andrevised by specification releases, which can span multiple years andspecify a breadth of new features and evolutions.

In one example, 3GPP introduced carrier aggregation (CA) for LTE inRelease 10. Although initially introduced with two downlink carriers,3GPP expanded carrier aggregation in Release 14 to include up to fivedownlink carriers and up to three uplink carriers. Other examples of newfeatures and evolutions provided by 3GPP releases include, but are notlimited to, License Assisted Access (LAA), enhanced LAA (eLAA),Narrowband Internet of things (NB-IOT), Vehicle-to-Everything (V2X), andHigh Power User Equipment (HPUE).

3GPP introduced Phase 1 of fifth generation (5G) technology in Release15, and plans to introduce Phase 2 of 5G technology in Release 16.Subsequent 3GPP releases will further evolve and expand 5G technology.5G technology is also referred to herein as 5G New Radio (NR).

5G NR supports or plans to support a variety of features, such ascommunications over millimeter wave spectrum, beamforming capability,high spectral efficiency waveforms, low latency communications, multipleradio numerology, and/or non-orthogonal multiple access (NOMA). Althoughsuch RF functionalities offer flexibility to networks and enhance userdata rates, supporting such features can pose a number of technicalchallenges.

The teachings herein are applicable to a wide variety of communicationsystems, including, but not limited to, communication systems usingadvanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro,and/or 5G NR.

FIG. 1 is a schematic diagram of one example of a communication network10. The communication network 10 includes a macro cell base station 1, asmall cell base station 3, and various examples of user equipment (UE),including a first mobile device 2 a, a wireless-connected car 2 b, alaptop 2 c, a stationary wireless device 2 d, a wireless-connected train2 e, a second mobile device 2 f, and a third mobile device 2 g.

Although specific examples of base stations and user equipment areillustrated in FIG. 1 , a communication network can include basestations and user equipment of a wide variety of types and/or numbers.

For instance, in the example shown, the communication network 10includes the macro cell base station 1 and the small cell base station3. The small cell base station 3 can operate with relatively lowerpower, shorter range, and/or with fewer concurrent users relative to themacro cell base station 1. The small cell base station 3 can also bereferred to as a femtocell, a picocell, or a microcell. Although thecommunication network 10 is illustrated as including two base stations,the communication network 10 can be implemented to include more or fewerbase stations and/or base stations of other types.

Although various examples of user equipment are shown, the teachingsherein are applicable to a wide variety of user equipment, including,but not limited to, mobile phones, tablets, laptops, IoT devices,wearable electronics, customer premises equipment (CPE),wireless-connected vehicles, wireless relays, and/or a wide variety ofother communication devices. Furthermore, user equipment includes notonly currently available communication devices that operate in acellular network, but also subsequently developed communication devicesthat will be readily implementable with the inventive systems,processes, methods, and devices as described and claimed herein.

The illustrated communication network 10 of FIG. 1 supportscommunications using a variety of cellular technologies, including, forexample, 4G LTE and 5G NR. In certain implementations, the communicationnetwork 10 is further adapted to provide a wireless local area network(WLAN), such as WiFi. Although various examples of communicationtechnologies have been provided, the communication network 10 can beadapted to support a wide variety of communication technologies.

Various communication links of the communication network 10 have beendepicted in FIG. 1 . The communication links can be duplexed in a widevariety of ways, including, for example, using frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). FDD is a type ofradio frequency communications that uses different frequencies fortransmitting and receiving signals. FDD can provide a number ofadvantages, such as high data rates and low latency. In contrast, TDD isa type of radio frequency communications that uses about the samefrequency for transmitting and receiving signals, and in which transmitand receive communications are switched in time. TDD can provide anumber of advantages, such as efficient use of spectrum and variableallocation of throughput between transmit and receive directions.

In certain implementations, user equipment can communicate with a basestation using one or more of 4G LTE, 5G NR, and WiFi technologies. Incertain implementations, enhanced license assisted access (eLAA) is usedto aggregate one or more licensed frequency carriers (for instance,licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensedcarriers (for instance, unlicensed WiFi frequencies).

As shown in FIG. 1 , the communication links include not onlycommunication links between UE and base stations, but also UE to UEcommunications and base station to base station communications. Forexample, the communication network 10 can be implemented to supportself-fronthaul and/or self-backhaul.

The communication links can operate over a wide variety of frequencies.In certain implementations, communications are supported using 5G NRtechnology over one or more frequency bands that are less than 6Gigahertz (GHz) and/or over one or more frequency bands that are greaterthan 6 GHz. For example, the communication links can serve FrequencyRange 1 (FR1), Frequency Range 2 (FR2), or a combination thereof.

For example, 5G NR can operate with different specifications acrossfrequency bands for 5G, including with flexible numerology compared withfixed numerology for 4G. FR1 includes existing and new bands andcorresponds to 450 MHz-6 GHz; sub-6 GHz bands with numerology subcarrierspacing of 15 kHz, 30 kHz and 60 kHz. Additionally, FR2 includes newbands and corresponds to millimeter wave frequencies of 24.25 GHz-52.6GHz with numerology subcarrier spacing of 60 kHz, 120 kHz and 240 kHz tobe able to handle higher phase noise and Doppler effects (for instance,for train applications up to 500 km/h).

In certain implementations, a base station and/or user equipmentcommunicates using beamforming. For example, beamforming can be used tofocus signal strength to overcome path losses, such as high lossassociated with communicating over high signal frequencies. In certainembodiments, user equipment, such as one or more mobile phones,communicate using beamforming on millimeter wave frequency bands in therange of 30 GHz to 300 GHz and/or upper centimeter wave frequencies inthe range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz. Inone embodiment, one or more of the mobile devices support a HPUE powerclass specification.

Different users of the communication network 10 can share availablenetwork resources, such as available frequency spectrum, in a widevariety of ways.

In one example, frequency division multiple access (FDMA) is used todivide a frequency band into multiple frequency carriers. Additionally,one or more carriers are allocated to a particular user. Examples ofFDMA include, but are not limited to, single carrier FDMA (SC-FDMA) andorthogonal FDMA (OFDMA). OFDMA is a multicarrier technology thatsubdivides the available bandwidth into multiple mutually orthogonalnarrowband subcarriers, which can be separately assigned to differentusers.

Other examples of shared access include, but are not limited to, timedivision multiple access (TDMA) in which a user is allocated particulartime slots for using a frequency resource, code division multiple access(CDMA) in which a frequency resource is shared amongst different usersby assigning each user a unique code, space-divisional multiple access(SDMA) in which beamforming is used to provide shared access by spatialdivision, and non-orthogonal multiple access (NOMA) in which the powerdomain is used for multiple access. For example, NOMA can be used toserve multiple users at the same frequency, time, and/or code, but withdifferent power levels.

Enhanced mobile broadband (eMBB) refers to technology for growing systemcapacity of LTE networks. For example, eMBB can refer to communicationswith a peak data rate of at least 10 Gbps and a minimum of 100 Mbps foreach user. Ultra-reliable low latency communications (uRLLC) refers totechnology for communication with very low latency, for instance, lessthan 2 milliseconds. uRLLC can be used for mission-criticalcommunications such as for autonomous driving and/or remote surgeryapplications. Massive machine-type communications (mMTC) refers to lowcost and low data rate communications associated with wirelessconnections to everyday objects, such as those associated with Internetof Things (IoT) applications.

The communication network 10 of FIG. 1 can be used to support a widevariety of advanced communication features, including, but not limitedto, eMBB, uRLLC, and/or mMTC.

FIG. 2A is a schematic diagram of one example of a communication linkusing carrier aggregation. Carrier aggregation can be used to widenbandwidth of the communication link by supporting communications overmultiple frequency carriers, thereby increasing user data rates andenhancing network capacity by utilizing fragmented spectrum allocations.

In the illustrated example, the communication link is provided between abase station 21 and a mobile device 22. As shown in FIG. 2A, thecommunications link includes a downlink channel used for RFcommunications from the base station 21 to the mobile device 22, and anuplink channel used for RF communications from the mobile device 22 tothe base station 21.

Although FIG. 2A illustrates carrier aggregation in the context of FDDcommunications, carrier aggregation can also be used for TDDcommunications.

In certain implementations, a communication link can provideasymmetrical data rates for a downlink channel and an uplink channel.For example, a communication link can be used to support a relativelyhigh downlink data rate to enable high speed streaming of multimediacontent to a mobile device, while providing a relatively slower datarate for uploading data from the mobile device to the cloud.

In the illustrated example, the base station 21 and the mobile device 22communicate via carrier aggregation, which can be used to selectivelyincrease bandwidth of the communication link. Carrier aggregationincludes contiguous aggregation, in which contiguous carriers within thesame operating frequency band are aggregated. Carrier aggregation canalso be non-contiguous, and can include carriers separated in frequencywithin a common band or in different bands.

In the example shown in FIG. 2A, the uplink channel includes threeaggregated component carriers f_(UL1), f_(UL2), and f_(UL3).Additionally, the downlink channel includes five aggregated componentcarriers f_(DL1), f_(DL2), f_(DL3), f_(DL4), and f_(DL5). Although oneexample of component carrier aggregation is shown, more or fewercarriers can be aggregated for uplink and/or downlink. Moreover, anumber of aggregated carriers can be varied over time to achieve desireduplink and downlink data rates.

For example, a number of aggregated carriers for uplink and/or downlinkcommunications with respect to a particular mobile device can changeover time. For example, the number of aggregated carriers can change asthe device moves through the communication network and/or as networkusage changes over time.

FIG. 2B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 2A. FIG. 2B includes a first carrieraggregation scenario 31, a second carrier aggregation scenario 32, and athird carrier aggregation scenario 33, which schematically depict threetypes of carrier aggregation.

The carrier aggregation scenarios 31-33 illustrate different spectrumallocations for a first component carrier f_(UL1), a second componentcarrier f_(UL2), and a third component carrier f_(UL3). Although FIG. 2Bis illustrated in the context of aggregating three component carriers,carrier aggregation can be used to aggregate more or fewer carriers.Moreover, although illustrated in the context of uplink, the aggregationscenarios are also applicable to downlink.

The first carrier aggregation scenario 31 illustrates intra-bandcontiguous carrier aggregation, in which component carriers that areadjacent in frequency and in a common frequency band are aggregated. Forexample, the first carrier aggregation scenario 31 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that are contiguousand located within a first frequency band BAND1.

With continuing reference to FIG. 2B, the second carrier aggregationscenario 32 illustrates intra-band non-continuous carrier aggregation,in which two or more components carriers that are non-adjacent infrequency and within a common frequency band are aggregated. Forexample, the second carrier aggregation scenario 32 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that arenon-contiguous, but located within a first frequency band BAND1.

The third carrier aggregation scenario 33 illustrates inter-bandnon-contiguous carrier aggregation, in which component carriers that arenon-adjacent in frequency and in multiple frequency bands areaggregated. For example, the third carrier aggregation scenario 33depicts aggregation of component carriers f_(UL1) and f_(UL2) of a firstfrequency band BAND1 with component carrier f_(UL3) of a secondfrequency band BAND2.

FIG. 2C illustrates various examples of downlink carrier aggregation forthe communication link of FIG. 2A. The examples depict various carrieraggregation scenarios 34-38 for different spectrum allocations of afirst component carrier f_(DL1), a second component carrier f_(DL2), athird component carrier f_(DL3), a fourth component carrier f_(DL4), anda fifth component carrier f_(DL5). Although FIG. 2C is illustrated inthe context of aggregating five component carriers, carrier aggregationcan be used to aggregate more or fewer carriers. Moreover, althoughillustrated in the context of downlink, the aggregation scenarios arealso applicable to uplink.

The first carrier aggregation scenario 34 depicts aggregation ofcomponent carriers that are contiguous and located within the samefrequency band. Additionally, the second carrier aggregation scenario 35and the third carrier aggregation scenario 36 illustrates two examplesof aggregation that are non-contiguous, but located within the samefrequency band. Furthermore, the fourth carrier aggregation scenario 37and the fifth carrier aggregation scenario 38 illustrates two examplesof aggregation in which component carriers that are non-adjacent infrequency and in multiple frequency bands are aggregated. As a number ofaggregated component carriers increases, a complexity of possiblecarrier aggregation scenarios also increases.

With reference to FIGS. 2A-2C, the individual component carriers used incarrier aggregation can be of a variety of frequencies, including, forexample, frequency carriers in the same band or in multiple bands.Additionally, carrier aggregation is applicable to implementations inwhich the individual component carriers are of about the same bandwidthas well as to implementations in which the individual component carriershave different bandwidths.

Certain communication networks allocate a particular user device with aprimary component carrier (PCC) or anchor carrier for uplink and a PCCfor downlink. Additionally, when the mobile device communicates using asingle frequency carrier for uplink or downlink, the user devicecommunicates using the PCC. To enhance bandwidth for uplinkcommunications, the uplink PCC can be aggregated with one or more uplinksecondary component carriers (SCCs). Additionally, to enhance bandwidthfor downlink communications, the downlink PCC can be aggregated with oneor more downlink SCCs.

In certain implementations, a communication network provides a networkcell for each component carrier. Additionally, a primary cell canoperate using a PCC, while a secondary cell can operate using a SCC. Theprimary and second cells may have different coverage areas, forinstance, due to differences in frequencies of carriers and/or networkenvironment.

License assisted access (LAA) refers to downlink carrier aggregation inwhich a licensed frequency carrier associated with a mobile operator isaggregated with a frequency carrier in unlicensed spectrum, such asWiFi. LAA employs a downlink PCC in the licensed spectrum that carriescontrol and signaling information associated with the communicationlink, while unlicensed spectrum is aggregated for wider downlinkbandwidth when available. LAA can operate with dynamic adjustment ofsecondary carriers to avoid WiFi users and/or to coexist with WiFiusers. Enhanced license assisted access (eLAA) refers to an evolution ofLAA that aggregates licensed and unlicensed spectrum for both downlinkand uplink.

FIG. 3A is a schematic diagram of one example of a downlink channelusing multi-input and multi-output (MIMO) communications. FIG. 3B isschematic diagram of one example of an uplink channel using MIMOcommunications.

MIMO communications use multiple antennas for simultaneouslycommunicating multiple data streams over common frequency spectrum. Incertain implementations, the data streams operate with differentreference signals to enhance data reception at the receiver. MIMOcommunications benefit from higher SNR, improved coding, and/or reducedsignal interference due to spatial multiplexing differences of the radioenvironment.

MIMO order refers to a number of separate data streams sent or received.For instance, MIMO order for downlink communications can be described bya number of transmit antennas of a base station and a number of receiveantennas for UE, such as a mobile device. For example, two-by-two (2×2)DL MIMO refers to MIMO downlink communications using two base stationantennas and two UE antennas. Additionally, four-by-four (4×4) DL MIMOrefers to MIMO downlink communications using four base station antennasand four UE antennas.

In the example shown in FIG. 3A, downlink MIMO communications areprovided by transmitting using M antennas 43 a, 43 b, 43 c, . . . 43 mof the base station 41 and receiving using N antennas 44 a, 44 b, 44 c,. . . 44 n of the mobile device 42. Accordingly, FIG. 3A illustrates anexample of m×n DL MIMO.

Likewise, MIMO order for uplink communications can be described by anumber of transmit antennas of UE, such as a mobile device, and a numberof receive antennas of a base station. For example, 2×2 UL MIMO refersto MIMO uplink communications using two UE antennas and two base stationantennas. Additionally, 4×4 UL MIMO refers to MIMO uplink communicationsusing four UE antennas and four base station antennas.

In the example shown in FIG. 3B, uplink MIMO communications are providedby transmitting using N antennas 44 a, 44 b, 44 c, . . . 44 n of themobile device 42 and receiving using M antennas 43 a, 43 b, 43 c, . . .43 m of the base station 41. Accordingly, FIG. 3B illustrates an exampleof n×m UL MIMO.

By increasing the level or order of MIMO, data bandwidth of an uplinkchannel and/or a downlink channel can be increased.

MIMO communications are applicable to communication links of a varietyof types, such as FDD communication links and TDD communication links.

FIG. 3C is schematic diagram of another example of an uplink channelusing MIMO communications. In the example shown in FIG. 3C, uplink MIMOcommunications are provided by transmitting using N antennas 44 a, 44 b,44 c, . . . 44 n of the mobile device 42. Additional a first portion ofthe uplink transmissions are received using M antennas 43 a 1, 43 b 1,43 c 1, . . . 43 m 1 of a first base station 41 a, while a secondportion of the uplink transmissions are received using M antennas 43 a2, 43 b 2, 43 c 2, . . . 43 m 2 of a second base station 41 b.Additionally, the first base station 41 a and the second base station 41b communication with one another over wired, optical, and/or wirelesslinks.

The MIMO scenario of FIG. 3C illustrates an example in which multiplebase stations cooperate to facilitate MIMO communications.

Examples of Envelope Controlled Radio Frequency Switches

Envelope tracking (ET) is a technique that can be used to increase poweradded efficiency (PAE) of a power amplifier by efficiently controlling avoltage level of a power amplifier supply voltage in relation to anenvelope of a radio frequency (RF) signal amplified by the poweramplifier. Thus, when the envelope of the RF signal increases, thevoltage supplied to the power amplifier can be increased. Likewise, whenthe envelope of the RF signal decreases, the voltage supplied to thepower amplifier can be decreased to reduce power consumption.

In certain embodiments herein, a power amplifier provides an RF signalto an antenna by way of an RF switch. Additionally, the envelope signalis used not only to control a power amplifier supply voltage of thepower amplifier, but also to control a regulated voltage used to turn onthe RF switch. For example, a level shifter can use a regulated voltagefrom charge pump circuitry to turn on the RF switch, and the envelopesignal can be provided to the charge pump circuitry and used to controlthe voltage level of the regulated voltage over time.

By using envelope tracking information to change the regulated voltagein this manner, the turn-on voltage of the RF switch tracksinstantaneous RF signal power. Thus, when the power of the RF signalincreases (as indicated by the envelope signal), the charge pumpcircuitry provides a corresponding change to the regulated voltage andthus to the turn-on voltage of the RF switch.

Implementing the turn-on voltage of the RF switch to track the envelopesignal provides a number of advantages, such as lower insertion loss,decreased on-state resistance, higher linearity, increased capacity,and/or superior third-order input intercept point (IIP3).

FIG. 4 is a schematic diagram of an RF switch system 120 according toone embodiment. The RF switch system 120 includes charge pump circuitry101, a level shifter 102, and an RF switch network 103.

In the illustrated embodiment, the RF switch network 103 includes aseries transistor switch 111 and a shunt transistor switch 115. As shownin FIG. 4 , the series transistor switch 111 is electrically connectedbetween an RF input terminal RF_IN and an RF output terminal RF_OUT, andthe shunt transistor switch 115 is electrically connected between the RFinput terminal RF_IN and ground. Although one example of an RF switchnetwork is shown, charge pumps can generate regulated voltages forcontrolling a wide variety of types of RF switch networks.

A power amplifier (not shown in FIG. 4 ) provides an RF signal to the RFinput terminal (RF_IN). In certain implementations, a power amplifiersupply voltage of the power amplifier is controlled by an envelopetracker that also receives the envelope signal ENVELOPE.

As shown in FIG. 4 , the charge pump circuitry 101 receives power by wayof a supply voltage VDD and ground, and operates to generate a positiveregulated voltage Vpos having a voltage level above the supply voltageVDD and a negative regulated voltage Vneg having a voltage level belowground.

The charge pump circuitry 101 also receives an envelope signal ENVELOPEthat indicates an envelope of the RF signal received at the RF inputterminal RF_IN. The charge pump circuitry 101 processes the envelopesignal ENVELOPE to control generation of one or more regulated voltages.For example, in certain implementations, the charge pump circuitry 101generates the positive regulated voltage V_(pos) to track or change withthe envelope signal ENVELOPE.

The level shifter 102 receives an input control signal IN forcontrolling a state of the RF switch network 103. In this example, thelevel shifter 102 generates a switch control voltage V_(CTL) forcontrolling the series transistor switch 111 and an inverted switchcontrol voltage V_(CTLB) for controlling the shunt transistor switch115.

In certain implementations, the level shifter 102 uses the positiveregulated voltage V_(pos) to generate the switch control voltage V_(CTL)in a first state of the input control signal IN, and uses the negativeregulated voltage V_(neg) to generate the switch control voltage V_(CTL)in a second state of the input control signal IN. Additionally, thelevel shifter 102 uses the negative regulated voltage V_(neg) togenerate the inverted switch control voltage V_(CTLB) in the first stateof the input control signal IN, and uses the positive regulated voltageV_(pos) to generate the inverted switch control voltage V_(CTLB) in thesecond state of the input control signal IN.

Thus, the positive regulated voltage V_(pos) and the negative regulatedvoltage V_(neg) are used to control the voltage levels of the switchcontrol voltage V_(CTL) and the inverted switch control voltage V_(CTLB)based on the state of the input control signal IN. Additionally, theswitch control voltage V_(CTL) and the inverted switch control voltageV_(CTLB) are inverted or complementary with respect to one another, inthis embodiment.

In certain implementations, the charge pump circuitry 101 uses theenvelope signal ENVELOPE to control the positive regulated voltageV_(pos). Thus, when the level shifter 102 sets the switch controlvoltage V_(CTL) be about equal to the positive regulated voltageV_(pos), the switch control voltage V_(CTL) tracks or changes with theenvelope signal ENVELOPE.

Implementing the RF switch system 120 in this manner provides a numberof advantages, including, but not limited to, lower insertion loss,decreased on-state resistance, higher linearity, increased capacity,and/or superior IIP3.

For instance, in one example, insertion loss (IL) of a transistor switchis given by Equation 1 below, where Ron is the on-state resistance ofthe transistor switch, Coff is the off-state capacitance of thetransistor switch, and Zo is the termination impedance of the transistorswitch.

$\begin{matrix}{{IL} = {10{\log\left\lbrack {\left( {1 + \frac{Ron}{2Zo}} \right)^{2} + \left( \frac{2\pi{{Coff}\left( {{Ron} + {Zo}} \right)}}{2} \right)^{2}} \right\rbrack}}} & {{Equation}1}\end{matrix}$

Additionally, in this example, third-order input intercept point (IIP3)of the transistor switch is given by Equation 2 below, where Isat is thesaturation current of the transistor switch, Ron is the on-stateresistance of the transistor switch, and Zo is the termination impedanceof the transistor switch.

$\begin{matrix}{{IIP3} = {{10{\log\left( \frac{Isa{t^{2}\left( {{Ron} + {2Zo}} \right)}^{4}}{4RonZo^{2}} \right)}} + {30}}} & {{Equation}2}\end{matrix}$

Furthermore, in this example, on-state resistance (Ron) of thetransistor switch is given by Equation 3 below, where w is the width ofthe transistor switch, l is the channel length of the transistor switch,μ is the channel carrier mobility of the transistor switch, Cox is thecapacitance density associated with the gate dielectric of thetransistor switch when turned on, Vth is the threshold voltage of thetransistor switch, n is a scaling factor, and Vpos is the voltage levelof the positive regulated voltage used to turn on the transistor switch.

$\begin{matrix}{{Ron} = {n\frac{1}{\mu Cox\frac{w}{l}\left( {{Vpos} - {Vth}} \right)}}} & {{Equation}3}\end{matrix}$

FIG. 5A is a schematic diagram of a positive charge pump 140 accordingto one embodiment. The positive charge pump 140 includes a charge pumpstage 131 and a filter 135.

The positive charge pump 140 illustrates one embodiment of a positivecharge pump suitable for generating a positive regulated voltage Vpos.However, the teachings herein are applicable to charge pump circuitryimplemented in a wide variety of ways.

The charge pump stage 131 includes a clock terminal CLK that receives aclock signal CLK, a ground terminal Gnd that receives a ground voltageor ground, a supply voltage terminal SUP that receives a supply voltageVDD, a negative voltage terminal Vn that receives ground, and a positivevoltage terminal Vp that outputs the positive regulated voltage Vpos.

In the illustrated embodiment, the envelope signal ENVELOPE is coupledto the positive regulated voltage Vpos by way of the filter 135. Incertain implementations, the filter 135 is implemented a low pass filtersuch that low frequency components of the envelope signal ENVELOPEmodulate the positive regulated voltage Vpos.

FIG. 5B is a schematic diagram of a charge pump stage 170 according toone embodiment. The charge pump stage 170 includes a first inverter 151,a second inverter 152, a third inverter 153, a first flying capacitor155, a second flying capacitor 156, a first p-type metal oxidesemiconductor (PMOS) transistor 161, a second PMOS transistor 162, afirst n-type metal oxide semiconductor (NMOS) transistor 163, and asecond NMOS transistor 164. The charge pump stage 170 includes a supplyvoltage terminal SUP, a ground voltage terminal GND, a clock terminalCLK, a positive voltage terminal Vp, and a negative voltage terminal Vn.

The charge pump stage 170 illustrates one embodiment of a charge pumpstage. However, the teachings herein are applicable to charge pumpcircuitry implemented in a wide variety of ways.

FIG. 6A is a schematic diagram of a positive charge pump 180 accordingto another embodiment. The positive charge pump 180 includes a firstcharge pump stage 131, a second charge pump stage 132, a first filter135, and a second filter 136.

The positive charge pump 180 illustrates another embodiment of apositive charge pump suitable for generating a positive regulatedvoltage Vpos. However, the teachings herein are applicable to chargepump circuitry implemented in a wide variety of ways.

The positive charge pump 180 of FIG. 6A is similar to the positivecharge pump 140 of FIG. 5A, except that the positive charge pump 180 isimplemented with an additional charge pump stage and an additionalfilter. Including multiple charge pump stages aids in further raisingthe voltage level of the positive regulated voltage Vpos above thesupply voltage VDD.

In the illustrated embodiment, the positive voltage terminal Vp of thefirst charge pump stage 131 outputs a stepped up voltage Vmid_up, whichserves as an input to the negative voltage terminal Vn of the secondcharge pump stage 132. Additionally, the positive voltage terminal Vp ofthe second charge pump stage 132 generates the positive regulatedvoltage Vpos. Although an example with two charge pump stages is shown,a charge pump can include more or fewer stages.

As shown in FIG. 6A, the clock terminal CLK of the first charge pumpstage 131 receives a first clock signal CLKA, while the clock terminalCLK of the second charge pump stage 132 receives a second clock signalCLKB. In certain implementations, the first clock signal CLKA and thesecond clock signal CLKB have about equal frequency but operate out ofphase with respect to one another to reduce switching noise.

In the illustrated embodiment, the stepped up voltage Vmid_up iselectrically connected to the first filter 135, and the positiveregulated voltage Vpos is electrically connected to the second filter136. Additionally, the envelope signal ENVELOPE is coupled to thestepped up voltage Vmid_up and the positive regulated voltage Vpos byway of the first filter 135 and the second filter 136, respectively.

FIG. 6B is a schematic diagram of one example of a ring oscillator 190for generating clock signals for a charge pump. The ring oscillator 190includes a first inverter 181, a second inverter 182, and a thirdinverter 183 that each receive power by way of a supply voltage VDD andground.

The positive charge pump 190 illustrates one embodiment of a clocksignal generator for a charge pump. However, the teachings herein areapplicable to charge pump circuitry implemented in a wide variety ofways.

As shown in FIG. 6B, the first inverter 181 receives a first clocksignal CLKA and outputs a second clock signal CLKB, the second inverter182 receives the second clock signal CLKB and outputs a third clocksignal CLKC, and the third inverter 183 receives the third clock signalCLKC and outputs the first clock signal CLKA.

FIG. 6C is one example of a timing diagram of clock signals for the ringoscillator 190 of FIG. 6B. The timing diagram includes example voltageversus time waveforms for the first clock signal CLKA, the second clocksignal CLKB, and the third clock signal CLKC of FIG. 6B.

FIG. 7 is a schematic diagram of a positive charge pump 220 according toanother embodiment. The positive charge pump 220 includes a first chargepump stage 131, a second charge pump stage 132, a first resistor 201, asecond resistor 202, a third resistor 203, a fourth resistor 204, afifth resistor 205, a first capacitor 211, a second capacitor 212, athird capacitor 213, and an envelope enable switch 218.

The positive charge pump 220 illustrates another embodiment of apositive charge pump suitable for generating a positive regulatedvoltage Vpos. However, the teachings herein are applicable to chargepump circuitry implemented in a wide variety of ways.

The positive charge pump 220 of FIG. 7 is similar to the positive chargepump 180 of FIG. 6A, except that the positive charge pump 220illustrates a specific implementation of filter circuitry for filteringthe stepped up voltage Vmid_up and the positive regulated voltage Vposand for injecting the envelope signal ENV.

In the illustrated embodiment, the first resistor 201 is electricallyconnected between the positive voltage terminal Vp of the first chargepump stage 131 and the stepped up voltage Vmid_up, which serves as aninput to the negative voltage terminal Vn of the second charge pumpstage 132. Additionally, the second resistor 202 is electricallyconnected between the envelope enable switch 218 and the stepped upvoltage Vmid_up, while the first capacitor 211 is electrically connectedbetween the stepped up voltage Vmid_up and ground.

Thus, when an envelope enable signal ENV_EN turns on the envelope enableswitch 218 to enable envelope control, the envelope signal ENVELOPE isinjected into the stepped up voltage Vmid_up by way of the secondresistor 202.

With continuing reference to FIG. 7 , the third resistor 203 iselectrically connected between a node 219 and the positive voltageterminal Vp of the second charge pump stage 132, while the fourthresistor 204 is electrically connected between the node 219 and thepositive regulated voltage Vpos. Additionally, the second capacitor 212is electrically connected between the positive regulated voltage Vposand ground, while the fifth resistor 205 and the third capacitor 213 areelectrically connected in series between the node 219 and the envelopeenable switch 218.

Thus, when the envelope enable switch 218 is turned on, the envelopesignal ENVELOPE is injected into the positive regulated voltage Vpos byway of the third capacitor 213, the fifth resistor 205, and the fourthresistor 204.

Including the third capacitor 213 aids in providing DC blocking, therebypreventing a flow of DC current between the positive regulated voltageVpos and the stepped up voltage Vmid_up.

FIG. 8 is a schematic diagram of a negative charge pump 260 according toone embodiment. The negative charge pump 260 includes a first chargepump stage 241, a second charge pump stage 242, a first filter resistor251, a second filter resistor 252, a first filter capacitor 253, and asecond filter capacitor 254.

The negative charge pump 260 illustrates one embodiment of a negativecharge pump suitable for generating a negative regulated voltage Vneg.However, the teachings herein are applicable to charge pump circuitryimplemented in a wide variety of ways.

In the illustrated embodiment, the positive voltage terminal Vp of thefirst charge pump stage 241 is electrically connected to ground, whilethe negative voltage terminal Vn of the first charge pump stage 241generates a stepped down voltage Vmid_dn, which serves as an input tothe positive voltage terminal Vp of the second charge pump stage 142.Although an example with two charge pump stages is shown, a charge pumpcan include more or fewer stages.

As shown in FIG. 8 , the clock terminal CLK of the first charge pumpstage 241 receives a first clock signal CLKA, while the clock terminalCLK of the second charge pump stage 242 receives a second clock signalCLKB. In certain implementations, the first clock signal CLKA and thesecond clock signal CLKB have about equal frequency but operate out ofphase with respect to one another.

In the illustrated embodiment, the first filter resistor 251 and thefirst filter capacitor 253 are electrically connected in series betweenthe stepped down voltage Vmid_dn and ground. Additionally, the secondfilter resistor 252 is electrically connected between the negativevoltage terminal Vn of the second charge pump stage 142 and the negativeregulated voltage Vneg, and the second filter capacitor 254 iselectrically connected between the negative regulated voltage Vneg andground.

FIG. 9 is a schematic diagram of a level shifter 350 according to oneembodiment. The level shifter 350 includes first to tenth NFETs 301-310,respectively, first to twelfth PFETs 311-322, respectively, first tofourth diodes 331-334, respectively, a first inverter 341, and a secondinverter 342. The first inverter 341 and the second inverter 342 arepowered by a supply voltage VDD and ground. Additionally, the levelshifter 350 receives a positive regulated voltage Vpos, a negativeregulated voltage Vneg, a stepped up voltage Vmid_up, and a stepped downvoltage Vmid_dn from charge pump circuitry. Furthermore, the levelshifter 350 receives an input control signal IN and an inverted inputcontrol signal INB, and generates a switch control voltage V_(CTL) andan inverted switch control voltage V_(CTLB).

The level shifter 350 illustrates one embodiment of the level shifter102 of FIG. 4 . However, the teachings herein are applicable to levelshifters implemented in other ways.

FIG. 10 is a schematic diagram of an RF switch network 420 according toanother embodiment. The RF switch network 420 includes a first seriestransistor switch 361, a second series transistor switch 365, a firstinput shunt transistor switch 381, a second input shunt transistorswitch 385, a first output shunt transistor switch 401, and a secondoutput shunt transistor switch 405.

The RF switch network 420 of FIG. 10 illustrates another embodiment ofan RF switch network suitable for use in an RF switch system, such asthe RF switch system 120 of FIG. 4 . However other implementations arepossible, including, but not limited, RF switch networks including moreor fewer series transistor switches and/or more or fewer shunttransistor switches.

In the illustrated embodiment, the first series transistor switch 361 iselectrically connected between a first RF input terminal RF_IN1 and anRF output terminal RF_OUT, and the second series transistor switch 365is electrically connected between a second RF input terminal RF_IN2 andthe RF output terminal RF_OUT. Additionally, the first input shunttransistor switch 381 is electrically connected between the first RFinput terminal RF_IN1 and ground, and the second input shunt transistor385 is electrically between the second RF input terminal RF_IN2 andground. Furthermore, the first output shunt transistor switch 401 iselectrically connected between the RF output terminal RF_OUT and ground,and the second output shunt transistor switch 405 is electricallyconnected between the RF output terminal RF_OUT and ground.

As shown in FIG. 10 , a first switch control voltage V_(CTL1) controlsthe first series transistor switch 361, and a first inverted switchcontrol voltage V_(CTLB1) controls the first input shunt transistorswitch 381 and the first output shunt transistor switch 401.Furthermore, a second switch control voltage V_(CTL2) controls thesecond series transistor switch 365, and a second inverted switchcontrol voltage V_(CTLB2) controls the second input shunt transistorswitch 385 and the second output shunt transistor switch 405. In certainimplementations, a first level shifter generates the first switchcontrol voltage V_(CTL1) and the first inverted switch control voltageV_(CTLB1), while a second level shifter generates the second switchcontrol voltage V_(CTL2) and the second inverted switch control voltageV_(CTLB2).

The depicted transistor switches each include a number of transistors inseries to achieve a desired power handling capability, with thetransistors biased used corresponding gate resistors and channelresistors.

For example, the first series transistor switch 361 includes NFETs 371a, 371 b, . . . 371 n, gate resistors 372 a, 372 b, . . . 372 n, andchannel resistors 373 a, 373 b, . . . 373 n. Additionally, the secondseries transistor switch 365 includes NFETs 375 a, 375 b, . . . 375 n,gate resistors 376 a, 376 b, . . . 376 n, and channel resistors 377 a,377 b, . . . 377 n. Furthermore, the first input shunt transistor switch381 includes NFETs 391 a, 391 b, gate resistors 392 a, 392 b, andchannel resistors 393 a, 393 b. Additionally, the second input shunttransistor switch 385 includes NFETs 395 a, 395 b, gate resistors 396 a,396 b, and channel resistors 397 a, 397 b. Furthermore, the first outputshunt transistor switch 401 includes NFETs 411 a, 411 b, gate resistors412 a, 412 b, and channel resistors 413 a, 413 b. Additionally, thesecond output shunt transistor switch 405 includes NFETs 415 a, 415 b,gate resistors 416 a, 416 b, and channel resistors 417 a, 417 b.

Examples of Envelope Tracking Calibration

Envelope tracking (ET) is a technique that can be used to increase poweradded efficiency (PAE) of a power amplifier by efficiently controlling avoltage level of a power amplifier supply voltage in relation to anenvelope of a radio frequency (RF) signal amplified by the poweramplifier. Thus, when the envelope of the RF signal increases, thevoltage supplied to the power amplifier can be increased. Likewise, whenthe envelope of the RF signal decreases, the voltage supplied to thepower amplifier can be decreased to reduce power consumption.

Schemes for aligning an envelope signal to a circuit that uses theenvelope signal are provided. In one example, the circuit correspond toan envelope tracker that controls the supply voltage of a poweramplifier in relation to the envelope signal. In a second example, thecircuit corresponds to a charge pump that controls a regulated voltage(for instance, for turning on an RF switch) in relation to the envelopesignal.

In certain embodiments, calibration is performed by providing anenvelope signal with a peak along an envelope path, and by providing anRF signal with a first peak and a second peak to a power amplifier alongan RF signal path. Additionally, an output of the power amplifier isobserved to generate an observation signal using an observationreceiver. The observation signal includes a first peak and a second peakcorresponding to the first peak and the second peak of the RF signal,and a delay between the envelope signal and the RF signal is controlledbased on relative size of the peaks of the observation signal to oneanother.

In certain implementations, the delay is controlled such that the peaksin the observation signal are of about equal size to one another.Additionally, the delay can be incremented or decremented untilalignment is achieved to a desired accuracy. Thus, an accurate and aflexible mechanism is provided for aligning an envelope signal to an RFsignal.

By calibrating envelope tracker delay in accordance with the teachingsherein, calibration can be achieved even when a duplexer and/or otherfront end component(s) have a narrow band frequency response. Incontrast, certain conventional envelope calibration schemes can sufferfrom inaccuracies and/or inability to calibrate when narrow bandcomponents are present along a path from the output of the poweramplifier to an observation receiver.

In certain implementations, a controllable delay circuit is programmedwith a delay generated based on the calibration. For example, acontrollable capacitor and/or other controllable delay circuit can havea setting selected based on the calibration. The setting can becontrolled based on analog and/or digital signals. For instance, a frontend system can include a memory and a controllable delay circuit that isprogrammed based on calibration data stored in the memory. In oneexample, the memory is a non-volatile memory programmed with datagenerated by a calibration sequence after manufacture or deployment in acommunication system, such as a mobile device. In a second example, thememory is volatile and is programmed with the calibration data over aserial interface, for instance, after power up.

The calibration can also be used to control a delay of multiplecomponents that operate based on the envelope signal. For example, afront end system can include an envelope tracker that controls a supplyvoltage of the power amplifier, and a charge pump that controls aregulated voltage for turning on an RF switch based on the envelopesignal. Additionally, calibration can be used to control a relativelydelay between the envelope signal being provided to the envelope trackerand envelope signal being provided to the charge pump.

FIG. 11 is a schematic diagram of one embodiment of a calibration schemefor a communication system 560 operating with envelope tracking. Thecommunication system 560 includes a baseband modem 501, a transceiver502, a front end module 503, and a power management integrated circuit(PMIC) 504.

In the illustrated embodiment, the baseband modem 501 includes acontrollable delay circuit 511, a look-up table 512, an envelopedigital-to-analog converter (DAC) 513, and an envelope filter 514. Thebaseband modem 501 operates to generate an in-phase (I) signal and aquadrature-phase (Q) signal along with an envelope signal Env(t)indicating the envelope of the RF signal represented by the I signal andthe Q signal. The controllable delay circuit 511 controls a delay of theenvelope signal Env(t).

With continuing reference to FIG. 11 , the transceiver 502 includes anI-path DAC 522 a, a Q-path DAC 522 b, an I-path baseband filter 523 a, aQ-path baseband filter 523 b, an I-path mixer 524 b, a Q-path mixer 524b, a local oscillator 525, a combiner 526, a controllable driver 527, afirst observation mixer 528 a, a second observation mixer 528 b, and anobservation receiver 530. The transceiver 502 processes the I signal andthe Q signal to generated an RF signal RF(t) that is amplified by thecontrollable driver 527 and thereafter provided to the front end module503.

The front end module 503 includes a power amplifier 541, a duplexer 542,a directional coupler 543, a low noise amplifier (LNA) 544, and anenvelope tracker 545. The power amplifier 541 amplifies the RF signalfrom the transceiver 502 and provides an RF output signal RF_OUT by wayof the duplexer 542 and directional coupler 543. The RF output signalRF_OUT is provided to an antenna (now shown in FIG. 11 ) fortransmission.

The power amplifier supply voltage V_(CC_PA) of the power amplifier 541is controlled by the envelope tracker 545 based on the envelope signalEnv(t) from the baseband modem 501. The envelope signal Env(t) is alsoprovide to the PMIC 504, which processes the envelope signal Env(t) togenerate one or more regulated voltage for the front end module 503.

With continuing reference to FIG. 11 , the directional coupler 543senses a reverse wave (RV) and a forward wave (FW), which aredownconverted by the first observation mixer 528 a and the secondobservation mixer 528 b, respectively, and subsequently processed by theobservation receiver 530.

The delay of the controllable delay circuit 511 controls a relativedelay or time difference between the envelope signal Env(t) and the RFsignal RF(t). Thus, the delay of the controllable delay circuit 511 canbe set to a value for aligning the RF signal and the power amplifiersupply voltage V_(CC_PA) at the power amplifier 541.

The delay of a controllable delay circuit (for instance, thecontrollable delay circuit 511) can be calibrated in accordance with theteachings herein to align an RF signal to an envelope controlled signal.For instance, an envelope controlled supply voltage to a power amplifiercan be aligned to an RF input signal to the power amplifier.

In the illustrated embodiment, the baseband modem 501 generates anenvelope signal 551 by way of an envelope path to the envelope tracker545. The envelope signal 551 includes a peak 552 and has a relativelylow bandwidth. In one example, during calibration, the envelope signal551 has a bandwidth of less than 1 MHz. Additionally, the baseband modemprovides an RF signal 553 having a first peak 554 a and a second peak554 b to the amplifier 541 by way of an RF signal path.

With continuing reference to FIG. 11 , the observation receiver 530captures an observation signal 555 from an output of the power amplifier541 by way of an observation path. The observation signal 555 includes afirst peak 556 a and a second peak 556 b.

In certain implementations, the delay of the controllable delay circuit511 is adjusted until the first peak 556 a and the second peak 556 b ofthe observation signal 555 are substantially equal, corresponding to anideal signal 557 having a first peak 558 a and a second peak 558 b thatare about equal to one another.

FIG. 12A is a schematic diagram of one embodiment of a front end module561 coupled to an antenna 562. The front end module 561 includes a poweramplifier 563, a power amplifier output matching network 564, a bandswitch 565, a first tuning route 566, a duplexer 567, a matching network568, a second tuning route 569, an antenna switch 570, a directionalcoupler 571, a differential envelope amplifier 572, a first envelopebuffer 573, a second envelope buffer 574, a third envelope buffer 575, afourth envelope buffer 576, a delay calibration circuit 577, and anenvelope tracker 578.

In the illustrated embodiment, an envelope signal (representeddifferentially as a difference between a non-inverted envelope signalEnv_p and an inverted envelope signal Env_n) is used to both control asupply voltage V_(CC_PA) of the power amplifier 563 and a regulatedvoltage of the antenna switch 570.

When the envelope signal is aligned to the envelope tracker 578, theenvelope signal may not be aligned to the antenna switch 570. Byincluding the delay calibration circuit 577, a desired delay between theenvelope signal arriving to the envelope tracker 578 and the envelopesignal arriving to the antenna switch 570 can be controlled.

FIG. 12B is a plot of one example of an in-band frequency response forthe duplexer 567 of the front end module 561 of FIG. 12A. As shown inFIG. 12B, the duplexer 567 can have a narrow band response and/or groupdelay effects that can complicate calibration for alignment between anRF signal and an envelope signal.

By calibrating envelope tracker delay in accordance with the teachingsherein, calibration can be achieved even when a duplexer and/or otherfront end component(s) have a narrow band response. Moreover, such afilter (such as an acoustic filter and/or a filter section of aduplexer) can be calibrated in accordance with the calibration schemesherein by sensing the signal before and after the filter and applyingcalibration coefficients into a transceiver (for instance, digitalpre-distortion coefficients). In contrast, certain conventional envelopecalibration schemes can suffer from inaccuracies and/or inability tocalibrate when narrow band components are present along a path from theoutput of the power amplifier to an observation receiver.

FIG. 13 is a schematic diagram of one embodiment of an envelope signalinterface 610. The envelope signal interface 610 includes a differentialinput envelope filter 601, a dual input differential amplifier 602, acurrent source 603, a load resistor 604, a first feedback resistor 605,a second feedback resistor 606, a feedback capacitor 607. Additionally,the differential input envelope filter 601 includes a first inputresistor 607, a second input resistor 608, and an input capacitor 609.

The differential input envelope filter 601 filters a differential inputsignal (In_p, In_n) to generate a differential envelop signal (Env_p,Env_n) that is provided to a first differential input of the dual inputdifferential amplifier 602. The dual input differential amplifier 602further includes an output that generates an envelope signal ENV, and afeedback loop from the output to a second differential input. Thefeedback operates to compensate for an error in a common voltage of thedifferential envelope signal. In certain implementations the currentsource 603 is controllable (for instance, variable and/or programmable)to control a common mode setting for providing common mode feedback.

The differential input envelope filter 601 can advantageously receive adifferential envelope signal in a sigma delta format. Thus, thedifferential input signal (In_p, In_n) can carry a sequence of pulses.Additionally, the resulting envelope signal ENV can be filtered torecover the envelope in an analog format, or processed to generate adigital representation of the envelope.

Accordingly, the envelope signal interface 610 provides flexibility ingenerating an envelope signal in analog or digital format as desired.

FIG. 14 is an annotated diagram of an envelope tracking system 621 inrelation to Shannon's theorem. The envelope tracking system 621 includesa power amplifier 622 that amplifies an RF input signal RF_(IN) togenerates an RF output signal RF_(OUT), and an envelope tracker 623powered by a battery voltage V_(BATT) and that controls a supply voltageV_(CC_PA) of the power amplifier 622 in relation to an envelope of theRF input signal RF_(IN).

As shown in FIG. 14 , annotations related to Shannon's theorem have beenprovided. In particular, an isotropic system 624 a with antennas 625 a,625 b, . . . 625 n and a combiner 626 is shown. Each of the antennas 625a, 625 b, . . . 625 n receives signal S, and the combiner 626 output3S(√3n). Additionally, an anisotropic system 624 b with antennas 625 a,625 b, . . . 625 n and a combiner 626 is also shown. Each of theantennas 625 a, 625 b, . . . 625 n receives signal S, and the combiner626 of the anisotropic system 624 b outputs eS/n.

ET techniques can be seen as an extension of the Shannon theory foranisotropic systems, where factor e represents the increase of theoutput signal when the envelope signal is aligned with the RF signalgoing into the power amplifier or other RF system.

The capacity of a wireless system as determined by Shannon formula isgiven in Equation 4 below.

$\begin{matrix}{C = {B_{w}{\sum\limits_{k = 1}^{k}{\log_{2}\left( {1 + \frac{en*S_{k}}{N_{x} + I_{k}}} \right)}}}} & {{Equation}4}\end{matrix}$

To achieve higher capacity following Equation 4, the channel bandwidthcan be increased, the spatial multiplexing level k can be raised throughMIMO, the noise Nx can be decreased through improved receivesensitivity, and/or in-band interference on link k can be reduced (forinstance, in multiple uplink transmit such as carrier aggregation andMIMO). Moreover, the channel capacity C can be increased through use ofenvelope tracking.

Examples of Radio Frequency Electronics with Envelope Tracking

Envelope tracking circuitry can be included in a wide variety of radiofrequency (RF) communication systems. Examples of such RF communicationsystems include, but are not limited to, mobile phones, tablets, basestations, network access points, customer-premises equipment (CPE),laptops, and wearable electronics. In certain implementations, envelopetracking circuitry can be included on a semiconductor die of a module,which in turn can be attached to a circuit board of an RF communicationsystem.

Although various examples of RF electronics with envelope tracking areprovided, the teachings herein are applicable to RF electronicsimplemented in a wide variety of ways. Accordingly, otherimplementations are possible.

FIG. 15 is a schematic diagram of a front end system 690 according toanother embodiment. The front end system 690 includes a front end module661, a diplexer 662, a directional coupler 663, an antenna tuningcircuit 664, a first antenna 665, and a second antenna 666.

In the illustrated embodiment, the front end system 690 includes aninput switch 671, a bypass switch 672, a power amplifier 673, an outputmatching circuit 674, a mode switch 675, a first tunable capacitor 676,a second tunable capacitor 677, a TDD transmit filter 678, a TDD receivefilter 679, an antenna switch 680, an FDD duplexer 681, a receive switch682, a low noise amplifier 683, an envelope amplifier 684, envelopetracker 685, and a digital interface circuit 686. In this example, thedigital interface circuit 686 is connected to a Mobile IndustryProcessor Interface (MIPI) serial peripheral interface (SPI) bus, whichis also connected to the antenna tuning circuit 664.

As shown in FIG. 15 , the antenna switch 680 includes a switch controlcircuit 687 that receives an envelope signal from the envelope amplifier684. In certain implementations, the switch control circuit 687 includescharge pump circuitry that generates a regulated voltage that iscontrolled by the envelope signal, and the regulated voltage is used toturn on one or more transistors used as switch elements in the antennaswitch 680. In the illustrated embodiment, the envelope signal is alsoprovided to the envelope tracker 685.

FIG. 16 is a schematic diagram of one embodiment of a mobile device 800.The mobile device 800 includes a baseband system 801, a transceiver 802,a front end system 803, antennas 804, a power management system 805, amemory 806, a user interface 807, and a battery 808.

The mobile device 800 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, 2G, 3G, 4G(including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (forinstance, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (forinstance, WiMax), and/or GPS technologies.

The transceiver 802 generates RF signals for transmission and processesincoming RF signals received from the antennas 804. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 16 as the transceiver 802. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 803 aids is conditioning signals transmitted toand/or received from the antennas 804. In the illustrated embodiment,the front end system 803 includes antenna tuning circuitry 810, poweramplifiers (PAs) 811, low noise amplifiers (LNAs) 812, filters 813,switches 814, and signal splitting/combining circuitry 815. However,other implementations are possible.

For example, the front end system 803 can provide a number offunctionalities, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or some combination thereof.

In certain implementations, the mobile device 800 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 804 can include antennas used for a wide variety of typesof communications. For example, the antennas 804 can include antennasfor transmitting and/or receiving signals associated with a wide varietyof frequencies and communications standards.

In certain implementations, the antennas 804 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 800 can operate with beamforming in certainimplementations. For example, the front end system 803 can includeamplifiers having controllable gain and phase shifters havingcontrollable phase to provide beam formation and directivity fortransmission and/or reception of signals using the antennas 804. Forexample, in the context of signal transmission, the amplitude and phasesof the transmit signals provided to the antennas 804 are controlled suchthat radiated signals from the antennas 804 combine using constructiveand destructive interference to generate an aggregate transmit signalexhibiting beam-like qualities with more signal strength propagating ina given direction. In the context of signal reception, the amplitude andphases are controlled such that more signal energy is received when thesignal is arriving to the antennas 804 from a particular direction. Incertain implementations, the antennas 804 include one or more arrays ofantenna elements to enhance beamforming.

The baseband system 801 is coupled to the user interface 807 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 801 provides the transceiver 802with digital representations of transmit signals, which the transceiver802 processes to generate RF signals for transmission. The basebandsystem 801 also processes digital representations of received signalsprovided by the transceiver 802. As shown in FIG. 16 , the basebandsystem 801 is coupled to the memory 806 of facilitate operation of themobile device 800.

The memory 806 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 800 and/or to provide storage of user information.

The power management system 805 provides a number of power managementfunctions of the mobile device 800. In certain implementations, thepower management system 805 includes a PA supply control circuit thatcontrols the supply voltages of the power amplifiers 811. For example,the power management system 805 can be configured to change the supplyvoltage(s) provided to one or more of the power amplifiers 811 toimprove efficiency, such as power added efficiency (PAE).

As shown in FIG. 16 , the power management system 805 receives a batteryvoltage from the battery 808. The battery 808 can be any suitablebattery for use in the mobile device 800, including, for example, alithium-ion battery.

FIG. 17 is a schematic diagram of one embodiment of a communicationsystem 1130 for transmitting RF signals. The communication system 1130includes a battery 1101, an envelope tracker 1102, a baseband processor1107, a signal delay circuit 1108, a digital pre-distortion (DPD)circuit 1109, an I/Q modulator 1110, an observation receiver 1111, anintermodulation detection circuit 1112, a power amplifier 1113, adirectional coupler 1114, a duplexing and switching circuit 1115, anantenna 1116, an envelope delay circuit 1121, a coordinate rotationdigital computation (CORDIC) circuit 1122, a shaping circuit 1123, adigital-to-analog converter 1124, and a reconstruction filter 1125.

The communication system 1130 of FIG. 17 illustrates one example of anRF system operating with a power amplifier supply voltage controlledusing envelope tracking. However, envelope tracking systems can beimplemented in a wide variety of ways.

The baseband processor 1107 operates to generate an I signal and a Qsignal, which correspond to signal components of a sinusoidal wave orsignal of a desired amplitude, frequency, and phase. For example, the Isignal can be used to represent an in-phase component of the sinusoidalwave and the Q signal can be used to represent a quadrature-phasecomponent of the sinusoidal wave, which can be an equivalentrepresentation of the sinusoidal wave. In certain implementations, the Iand Q signals are provided to the I/Q modulator 1110 in a digitalformat. The baseband processor 1107 can be any suitable processorconfigured to process a baseband signal. For instance, the basebandprocessor 1107 can include a digital signal processor, a microprocessor,a programmable core, or any combination thereof.

The signal delay circuit 1108 provides adjustable delay to the I and Qsignals to aid in controlling relative alignment between the envelopesignal and the RF signal RF_(IN). The amount of delay provided by thesignal delay circuit 1108 is controlled based on amount ofintermodulation detected by the intermodulation detection circuit 1112.

The DPD circuit 1109 operates to provide digital shaping to the delayedI and Q signals from the signal delay circuit 1108 to generate digitallypre-distorted I and Q signals. In the illustrated embodiment, thepre-distortion provided by the DPD circuit 1109 is controlled based onamount of intermodulation detected by the intermodulation detectioncircuit 1112. The DPD circuit 1109 serves to reduce a distortion of thepower amplifier 1113 and/or to increase the efficiency of the poweramplifier 1113.

The I/Q modulator 1110 receives the digitally pre-distorted I and Qsignals, which are processed to generate an RF signal RF_(IN). Forexample, the I/Q modulator 1110 can include DACs configured to convertthe digitally pre-distorted I and Q signals into an analog format,mixers for upconverting the analog I and Q signals to radio frequency,and a signal combiner for combining the upconverted I and Q signals intoan RF signal suitable for amplification by the power amplifier 1113. Incertain implementations, the I/Q modulator 1110 can include one or morefilters configured to filter frequency content of signals processedtherein.

The envelope delay circuit 1121 delays the I and Q signals from thebaseband processor 1107. Additionally, the CORDIC circuit 1122 processesthe delayed I and Q signals to generate a digital envelope signalrepresenting an envelope of the RF signal RF_(IN). Although FIG. 17illustrates an implementation using the CORDIC circuit 1122, an envelopesignal can be obtained in other ways.

The shaping circuit 1123 operates to shape the digital envelope signalto enhance the performance of the communication system 1130. In certainimplementations, the shaping circuit 1123 includes a shaping table thatmaps each level of the digital envelope signal to a corresponding shapedenvelope signal level. Envelope shaping can aid in controllinglinearity, distortion, and/or efficiency of the power amplifier 1113.

In the illustrated embodiment, the shaped envelope signal is a digitalsignal that is converted by the DAC 1124 to an analog envelope signal.Additionally, the analog envelope signal is filtered by thereconstruction filter 1125 to generate an envelope signal suitable foruse by the envelope tracker 1102. In certain implementations, thereconstruction filter 1125 includes a low pass filter.

With continuing reference to FIG. 17 , the envelope tracker 1102receives the envelope signal from the reconstruction filter 1125 and abattery voltage V_(BATT) from the battery 1101, and uses the envelopesignal to generate a power amplifier supply voltage V_(CC_PA) for thepower amplifier 1113 that changes in relation to the envelope of the RFsignal RF_(IN). The power amplifier 1113 receives the RF signal RF_(IN)from the I/Q modulator 1110, and provides an amplified RF signalRF_(OUT) to the antenna 1116 through the duplexing and switching circuit1115, in this example.

The directional coupler 1114 is positioned between the output of thepower amplifier 1113 and the input of the duplexing and switchingcircuit 1115, thereby allowing a measurement of output power of thepower amplifier 1113 that does not include insertion loss of theduplexing and switching circuit 1115. The sensed output signal from thedirectional coupler 1114 is provided to the observation receiver 1111,which can include mixers for down converting I and Q signal componentsof the sensed output signal, and DACs for generating I and Q observationsignals from the downconverted signals.

The intermodulation detection circuit 1112 determines an intermodulationproduct between the I and Q observation signals and the I and Q signalsfrom the baseband processor 1107. Additionally, the intermodulationdetection circuit 1112 controls the pre-distortion provided by the DPDcircuit 1109 and/or a delay of the signal delay circuit 1108 to controlrelative alignment between the envelope signal and the RF signalRF_(IN). In certain implementations, the intermodulation detectioncircuit 1112 also serves to control shaping provided by the shapingcircuit 1123.

By including a feedback path from the output of the power amplifier 1113and baseband, the I and Q signals can be dynamically adjusted tooptimize the operation of the communication system 1130. For example,configuring the communication system 1130 in this manner can aid inproviding power control, compensating for transmitter impairments,and/or in performing DPD.

Although illustrated as a single stage, the power amplifier 1113 caninclude one or more stages. Furthermore, the teachings herein areapplicable to communication systems including multiple power amplifiers.In such implementations, separate envelope trackers can be provided fordifferent power amplifiers and/or one or more shared envelope trackerscan be used.

FIG. 18 is a schematic diagram of one example of a power amplifiersystem 1140 including an envelope tracker 1102. The illustrated poweramplifier system 1140 further includes an inductor 1127, an outputimpedance matching circuit 1131, and a power amplifier 1132. Theillustrated envelope tracker 1102 receives a battery voltage V_(BATT)and an envelope of the RF signal and generates a power amplifier supplyvoltage V_(CC_PA) for the power amplifier 1132.

The illustrated power amplifier 1132 includes a bipolar transistor 1129having an emitter, a base, and a collector. As shown in FIG. 18 , theemitter of the bipolar transistor 1129 is electrically connected to apower low supply voltage V₁, which can be, for example, a ground supply.Additionally, an RF signal (RF_(IN)) is provided to the base of thebipolar transistor 1129, and the bipolar transistor 1129 amplifies theRF signal to generate an amplified RF signal at the collector. Thebipolar transistor 1129 can be any suitable device. In oneimplementation, the bipolar transistor 1129 is a heterojunction bipolartransistor (HBT).

The output impedance matching circuit 1131 serves to terminate theoutput of the power amplifier 1132, which can aid in increasing powertransfer and/or reducing reflections of the amplified RF signalgenerated by the power amplifier 1132. In certain implementations, theoutput impedance matching circuit 1131 further operates to provideharmonic termination and/or to control a load line impedance of thepower amplifier 1132.

The inductor 1127 can be included to provide the power amplifier 1132with the power amplifier supply voltage V_(CC_PA) generated by theenvelope tracker 1102 while choking or blocking high frequency RF signalcomponents. The inductor 1127 can include a first end electricallyconnected to the envelope tracker 1102, and a second end electricallyconnected to the collector of the bipolar transistor 1129. In certainimplementations, the inductor 1127 operates in combination with theimpedance matching circuit 1131 to provide output matching.

Although FIG. 18 illustrates one implementation of the power amplifier1132, skilled artisans will appreciate that the teachings describedherein can be applied to a variety of power amplifier structures, suchas multi-stage power amplifiers and power amplifiers employing othertransistor structures. For example, in some implementations the bipolartransistor 1129 can be omitted in favor of employing a field-effecttransistor (FET), such as a silicon FET, a gallium arsenide (GaAs) highelectron mobility transistor (HEMT), or a laterally diffused metal oxidesemiconductor (LDMOS) transistor. Additionally, the power amplifier 1132can be adapted to include additional circuitry, such as biasingcircuitry.

FIGS. 13A and 13B show two examples of power amplifier supply voltageversus time.

In FIG. 19A, a graph 1147 illustrates one example of the voltage of anRF signal 1141 and a power amplifier supply voltage 1143 versus time.The RF signal 1141 has an envelope 1142.

It can be important that the power amplifier supply voltage 1143 of apower amplifier has a voltage greater than that of the RF signal 1141.For example, powering a power amplifier using a power amplifier supplyvoltage that has a magnitude less than that of the RF signal can clipthe RF signal, thereby creating signal distortion and/or other problems.Thus, it can be important the power amplifier supply voltage 1143 begreater than that of the envelope 1142. However, it can be desirable toreduce a difference in voltage between the power amplifier supplyvoltage 1143 and the envelope 1142 of the RF signal 1141, as the areabetween the power amplifier supply voltage 1143 and the envelope 1142can represent lost energy, which can reduce battery life and increaseheat generated in a wireless device.

In FIG. 19B, a graph 1148 illustrates another example of the voltage ofan RF signal 1141 and a power amplifier supply voltage 1144 versus time.In contrast to the power amplifier supply voltage 1143 of FIG. 19A, thepower amplifier supply voltage 1144 of FIG. 19B changes in relation tothe envelope 1142 of the RF signal 1141. The area between the poweramplifier supply voltage 1144 and the envelope 1142 in FIG. 19B is lessthan the area between the power amplifier supply voltage 1143 and theenvelope 1142 in FIG. 19A, and thus the graph 1148 of FIG. 19B can beassociated with a power amplifier system having greater energyefficiency.

CONCLUSION

Some of the embodiments described above have provided examples inconnection with mobile devices. However, the principles and advantagesof the embodiments can be used for any other systems or apparatus thathave needs for envelope tracking.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“may,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A radio frequency front end system comprising: apower amplifier configured to amplify a radio frequency signal togenerate a radio frequency output signal, the power amplifier configuredto receive power from a power amplifier supply voltage; an envelopetracker configured to control a voltage level of the power amplifiersupply voltage based on an envelope signal indicating an envelope of theradio frequency signal; a radio frequency switch configured to receivethe radio frequency output signal; a charge pump configured to control aregulated voltage for the radio frequency switch based on the envelopesignal; and a controllable delay circuit operable to control a delaybetween the envelope signal arriving to the charge pump and the envelopesignal arriving to the envelope tracker, the delay calibrated bycalibration data.
 2. The radio frequency front end system of claim 1further comprising a directional coupler configured to generate anobservation signal based on observing an output of the power amplifier.3. The radio frequency front end system of claim 2 further comprising anobservation receiver coupled to the radio frequency front end system,the observation receiver configured to generate the calibration databased on the observation signal.
 4. The radio frequency front end systemof claim 3 wherein the observation receiver is further configured togenerate the calibration data based on comparing a first peak of theobservation signal to a second peak of the observation signal.
 5. Theradio frequency front end system of claim 4 wherein the first peak andthe second peak are substantially triangular.
 6. The radio frequencyfront end system of claim 4 wherein the observation receiver is furtherconfigured to generate the calibration data based on changing the delayuntil a size of the first peak is substantially equal to a size of thesecond peak.
 7. The radio frequency front end system of claim 1 furthercomprising a memory storing the calibration data.
 8. The radio frequencyfront end system of claim 1 further comprising a duplexer connectedbetween the power amplifier and the radio frequency switch.
 9. A mobiledevice comprising: a transceiver configured to generate a radiofrequency signal; and a radio frequency front end system including apower amplifier configured to amplify the radio frequency signal togenerate a radio frequency output signal, an envelope tracker configuredto control a voltage level of a power amplifier supply voltage of thepower amplifier based on an envelope signal indicating an envelope ofthe radio frequency signal, a radio frequency switch configured toreceive the radio frequency output signal, a charge pump configured tocontrol a regulated voltage for the radio frequency switch based on theenvelope signal, and a controllable delay circuit operable to control adelay between the envelope signal arriving to the charge pump and theenvelope signal arriving to the envelope tracker, the delay calibratedby calibration data.
 10. The mobile device of claim 9 wherein the radiofrequency front end system further includes a directional couplerconfigured to generate an observation signal based on observing anoutput of the power amplifier.
 11. The mobile device of claim 10 whereinthe transceiver further includes an observation receiver configured togenerate the calibration data based on the observation signal.
 12. Themobile device of claim 11 wherein the observation receiver is furtherconfigured to generate the calibration data based on comparing a firstpeak of the observation signal to a second peak of the observationsignal.
 13. The mobile device of claim 12 wherein the first peak and thesecond peak are substantially triangular.
 14. The mobile device of claim12 wherein the observation receiver is further configured to generatethe calibration data based on changing the delay until a size of thefirst peak is substantially equal to a size of the second peak.
 15. Themobile device of claim 9 wherein the radio frequency front end systemfurther includes a memory storing the calibration data.
 16. The mobiledevice of claim 9 wherein the radio frequency front end system furtherincludes a duplexer connected between the power amplifier and the radiofrequency switch.
 17. The mobile device of claim 9 further comprising anantenna configured to transmit the radio frequency output signal.
 18. Amethod of envelope alignment, the method comprising: amplifying a radiofrequency signal to generate a radio frequency output signal using apower amplifier, controlling a voltage level of a power amplifier supplyvoltage of the power amplifier based on an envelope signal using anenvelope tracker, the envelope signal indicating an envelope of theradio frequency signal; receiving the radio frequency output signal asan input to a radio frequency switch, the radio frequency switchcontrolled by a regulated voltage; controlling the regulated voltagebased on the envelope signal using a charge pump; controlling a delaybetween the envelope signal arriving to the charge pump and the envelopesignal arriving to the envelope tracker using a controllable delaycircuit; and calibrating the delay using calibration data.
 19. Themethod of claim 18 further comprising generating an observation signalbased on observing an output of the power amplifier using a directionalcoupler.
 20. The method of claim 19 further comprising generating thecalibration data based on the observation signal using an observationreceiver.